Search

Abstract: Many efforts have been made in order to adequate the production of a solar thermal collector field to the consumption of domestic hot water of the inhabitants of a building. In that sense, much has been achieved in different domains: research agencies, government policies and manufacturers. However, most of the design rules of the solar plants are based on steady state models, whereas solar irradiance, consumption and thermal accumulation are inherently transient processes. As a result of this lack of physical accuracy, thermal storage tanks are sometimes left to be as large as the designer decides without any aforementioned precise recommendation. This can be a problem if solar thermal systems are meant to be implemented in nowadays buildings, where there is a shortage of space. In addition to that, an excessive storage volume could not result more efficient in many residential applications, but costly, extreme in space consumption and in some cases too heavy. A proprietary transient simulation program has been developed and validated with a detailed measurement campaign in an experimental facility. In situ environmental data have been obtained through a whole year of operation. They have been gathered at intervals of 10min for a solar plant of 50m2 with a storage tank of 3m3, including the equipment for domestic hot water production of a typical apartment building. This program has been used to obtain the design and dimensioning criteria of DHW solar plants under daily transient conditions throughout a year and more specifically the size of the storage tank for a multi storey apartment building. Comparison of the simulation results with the current Spanish regulation applicable, “Código Técnico de la Edificación” (CTE 2006), offers fruitful details and establishes solar facilities dimensioning criteria. [Copyright &y& Elsevier]

Abstract: This study has been carried out with a building experimental solar facility based on a 9-year-old field of 50m2 flat plate solar collectors located south of Madrid, Spain. Building domestic hot water production and heating and cooling applications were implemented in the facility. Experimental data corresponding to 100 operating variables (mainly temperatures and flow rates) were recorded during an entire year at intervals of 10min, and from this data, all of the relevant performance parameters were derived. Three thermocouples measured the centre point instantaneous temperatures of the glass cover, the box back surface and the absorber plate of one of the collectors. A 1D collector transient model, based on thermal resistances and capacitances, has been developed and validated with the experimental database. Both experimental and modelled collector thermal energy output and outlet temperatures were obtained under instantaneous real operating conditions. The individual effect on the drop of the thermal energy output can be summarised in the following yearly averaged values: 15.0% due to collector surface aging, 15.7% due to thermal loss produced by wind velocity magnitude and direction, ±3.2% variations due to thermal capacitance and 7.6% due to incident angle of irradiance. Finally, the repercussions on the performance of the real applications are discussed. [Copyright &y& Elsevier]

Abstract: This paper presents the analysis of the performance of a solar cooling facility along one summer season using a commercial single-effect water–lithium bromide absorption chiller aiming at domestic applications. The facility works only with solar energy using flat plate collectors and it is located at Universidad Carlos III de Madrid, Spain. The statistical analysis performed with the gathered data shows the influence of five daily operational variables on the system performance. These variables are solar energy received along the day (H) and the average values, along the operating period of the solar cooling facility (from sunrise to the end of the cold-water production), of the ambient temperature (), the wind velocity magnitude (V), the wind direction (θ) and the relative humidity (RH). First order correlation functions are given. The analysis of the data allows concluding that the most influential variables on the daily cooling energy produced and the daily averaged solar COP are H, V and θ. The period length of cold-water production is determined mainly by H and . [ABSTRACT FROM AUTHOR]

Abstract: Various researchers have developed models of conventional H2O–LiBr absorption machines with the aim of predicting their performance. In this paper, the methodology of characteristic equations developed by is applied. This model is able to represent the capacity of single effect absorption chillers and heat pumps by means of simple algebraic equations. An extended characteristic equation based on a characteristic temperature difference has been obtained, considering the facility features. As a result, it is concluded that for adiabatic absorbers a subcooling temperature must be specified. The effect of evaporator overflow has been characterized. Its influence on cooling capacity has been included in the extended characteristic equation. Taking into account the particular design and operation features, a good agreement between experimental performance data and those obtained through the extended characteristic equation has been achieved at off-design operation. This allows its use for simulation and control purposes. [Copyright &y& Elsevier]

Abstract: A facility for experimental evaluation of innovative components forming part of a single effect LiBr–H2O adiabatic absorption chiller is described. Plate heat exchangers have been incorporated in the design. Two adiabatic absorber configurations, droplets and liquid sheets, were designed and tested and its performances parameters were experimentally determined. Evaporator limitations have been identified and included in the analysis. Liquid accumulation leads to overflow of refrigerant out of the evaporators. Some general observations, regarding particular operating conditions, are reported. The absorber performance has been characterized in terms of heat and mass transfer through the heat conductance and the effectiveness. The influence of the recirculation ratio is presented for both cases. The liquid sheet configuration has shown better evaluation parameters than droplets configuration. A significant reduction in the absorber size (up to 50%) as compared to using droplets is possible. [Copyright &y& Elsevier]